Photographic diffusion transfer process



April 30, 1963 E. H. LAND 3,087,816

' PHOTOGRAPHIC DIFFUSION TRANSFER PROCESS Filed April 1, 1955 Processing Composi'l'ion Including Silver Halide Developer and Silver Halide Solvenl' Supporl' Phol'osensifive Silver Halide Sl'ra'l'um lver-Recep'live Slralum upporl' FIG. I

Spread and Expose Layer of Processina Composil'ion Spread Firsl Phol'osensil'ive S'l'ralum Then Phol'oexposed Posilive Prinl Forms Sponl'aneously AHer Phol'oexposure of Pho'l'osens il'ive Sl'ralum I N VEN TOR.

ATTORNEYS United Sites Patent 61 Corporation, Cambridge, Mass., a corporation of Delaware Filed Apr. 1, 1955, Ser. No. 498,672. 1 Claim. (CI. 96-29) This invention relates to photography and, more par ticularly, to photographic processes of the type in which a processing composition is spread between a pair of superposed elements, one of which is photosensitive.

This invention contemplates first spreading a processmg composition between a photosensitive stratum and an auxiliary stratum, one of which is transparent, and then photoexposing the photosensitive stratum to form a latent image that develops spontaneously. In one of its variety of novel applications, this invention may be effected by a film unit which comprises a photosensitive sheet, another sheet and a container of processing composition to be spread between them in response to a single movement of the film unit into the exposure chamber of a camera. There, the photosensitive sheet, immediately after development has :been initiated, is photoexposed to produce a latent image from which a print is formed without further manipulation or treatment.

This invention is applicable to a variety of processes involving the formation of latent images in dispersions of heavy metal salts such as the noble metal salts, particularly the silver halides. It is particularly applicable to processes of the silver transfer-reversal type. In one such process, as will be described more specifically below, a composition comprising an aqueous alkaline solution of a silver halide developer and a silver halide solvent is spread in a layer between a pair of sheets, one of which carries a stratum containing a gelatino silver halide emulsion and one of which is transparent. Immediately thereafter, the stratum is photoexposed to a subject through the transparent sheet. The reagents develop exposed silver halide to silver and react with unreduced silver halide to form a soluble silver complex which, when reduced to silver on one of the sheets or in the layer ot solution, forms a positive print. Finally, the sheets are stripped apart to make the positive print available for use.

Accordingly, the primary objects of this invention are: to provide a process which comprises the steps of superposing a photosensitive stratum and an auxiliary stratum, one of which is transparent, the photosensitive stratum containing a heavy metal salt which gives a latent response when subjected to actinic radiation, spreading a processing composition in a thin layer between the strata, the processing composition containing a heavy metal salt developer that selectively reduces exposed heavy metal salt to heavy metal and photoexposing the photosensitive stratum while the strata are superposed to form a latent image that develops spontaneously; and to provide processing compositions useful in such processes and containing hypersensitizers or optical sensitizers.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the composition of matter possessing the features and properties which are exemplified in the following detailed disclosure and the several steps and the relation and order of one or more of such steps with respect to each of the others, and the scope of the application of which will be indicated in the claim.

For a fuller understanding of the nature and objects of the invention, reference should be had to the follow- "ice ing detailed description taken in connection with the accompanying drawing wherein:

FIGURE 1 is an exaggerated sectional view of a film unit designed to effect a process of the silver transfer-' reversal type in accordance with the present invention; and

FIGS. 2 and 3 are exaggerated sectional views of the film unit of FIG. 1 in operation.

The film unit of FIG. -1 comprises a photosensitive sheet including a support 10 and a gelatino silver halide stratum 12, a print-receptive sheet including a support 14 and a silver-receptive stratum .16, and a container 18 carrying an alkaline aqueous solution 20 of a silver halide developer and a silver halide solvent. FIG. 2 shows the film unit after solution 20* has been spread between the sheets, for example by advancing the film unit between the pair of pressure-applying rollers. Immediately after solution 20 is spread, photosensitive stratum 12 is exposed through the lens of a camera. Ordinarily, it is desired that photoexposure occur soon enough after spreading in order to avoid desensitization of the photosensitive material by the solution as, for example, one second or less thereafter. Thereafter, solution 20, within a predetermined period, reduces silver halide to silver in stratum 12 to form a negative print and reacts with unreduced silver halide to form a complex silver salt which difiuses through the layer of solution to stratum 16 where it is reduced to silver to form a positive print. Finally, as shown in FIG. 3, stratum 12, together with the layer of solution, is stripped from stratum 16 to render the positive print available for use. Alternatively, as disclosed in copending application Serial No. 466,889, filed November 4, 1954 (US. Patent No. 2,861,885), in the name of Edwin H. Land, where the covering power of silver in stratum 16 is much greater than the covering power of silver in stratum 12, the composite print comprising both the negative of stratum 12 and the positive of stratum 16 is useful without stripping.

Composition 20, for example, contains a silver halide developer such as hydroquinone, a silver halide solvent such as sodium thiosulfate and a film-forming material such as a Water-soluble polymer, e.g., a plastic, starch or gum, or an insoluble emulsifiable oil which imparts to the solution a viscosity ranging from to 200,000 centipoises at 20 C.

A novel aspect of this invention of particular importance concerns high-speed photography where latent image regression is sought to be minimized. It has been found that prints of high pictorial quality may be pro duced by silver transfer-reversal in the foregoing manner from negative silver halide emulsion having speeds in excess of 100 A.S.A.

In one composition useful in the process of the present invention, a hypersensitizer or optical sensitizer is incorporated in processing composition 20. When spread, such a composition imparts to photosensitive stratum 12 a special sensitivity at the same time that it initiates silver transfer-reversal. Suitable hypersensitizing agents for example, are ammonia, a thiourea such as palmityl thiourea or styrene fumaryl allyl thiourea, allyl isothiocyanate, thiazole, quinoline and pyridine. Suitable optical sensitizing agents, for example, are dyes such as derivatives of fluorescein including erythrosine and eosin and various cyanines such as thiazole, thiazoline, pyridine, benzooxazole, benzothiazole, benzoselenazole, 3,3 dimethyl indolenine, naphtho-Z-l-thiazole and naphtho-l-Z- diazole. The incorporation of such a material in solution 20 is advantageous because its action, which may be of short duration, is initiated immediately before stratum 12 is photoexposed.

Water 1860 Sodium carboxymethyl cellulose 93.0 Sodium sulfite 78.0 Sodium hydroxide 54.6 Sodium thiosulfate 14.5 Hydroquinone 52.0

Less than a second after the spreading of composition 20 is completed, silver halide stratum 12 is photoexposed. Thereafter, silver halide stratum -12 and silver-receptive stratum 16 are maintained in superposed relation with composition 20 therebetween for a period of the order of 40 to 120 seconds in duration. At the end of this period, the silver halide stratum, together with composition 20, is stripped from the silver-receptive stratum .16 to display a positive print of high quality.

,In a modification of the film unit of FIG. 1, the positive print is formed in the layer of processing composition rather than in the silver-receptive stratum. The processing composition includes, in addition to the silver halide developer and the silver halide solvent, silver precipitating nuclei as disclosed in Patent No. 2,662,822, issued to Edwin H. Land on December 15, 1953, and silver-receptive stratum 16 is omitted. Here, after processing has been effected, support 14, together with the layer of processing composition in which a positive print has formed, is stripped from photosensitive silver halide stratum 12 and its support 10.

In another modification of the film unit of FIG. 1, the outer face of support 14 of the silver-receptive sheet, which in this instance is transparent, is provided with an optical screen, for example one of the lenticulated or additive color type. After spreading is effected between the inner face of the print-receptive sheet and photosensitive stratum 12, the latter is photoexposed through the screen. The resulting print, which forms either in silver-receptive stratum 16 or in layer of solution 20 when it incorporates silver precipitating nuclei, is automatically aligned with the screen through which the image is viewed.

The present invention thus contemplates compositions and processes involved in the spreading of a processing composition and the photoexposing of the photosensitive stratum which it then contacts to produce a latent im- 4 age from which a visible image is spontaneously produced without additional manipulation or treatment.

Since certain changes may be made in the above compositions and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

The photographic process comprising a first group of steps including superposing a pair of sheets and spreading a processing composition therebetween and in contact therewith to form a sandwich by advancing said sheets, with said composition therebetween, between a pair of pressure-applying rollers, one sheet of said pair having a photosensitive stratum, said sandwich being transparent at least from one of its outer faces through to the surface of the adjacent face of said photosensitive stratum, said photosensitive stratum containing a silver halide salt which gives a latent response when subjected to actinic radiation, said composition containing an aqueous alkaline solution including a silver halide developer and a silver halide solvent, said composition also containing a member of the class consisting of the silver halide hypersensitizers and the silver halide optical sensitizers, and, immediately thereafter, photoex osing said silver halide salt, the first group of steps automatically initiating a second group of steps including reacting said silver halide developer with exposed silver halide to reduce said exposed silver halide to silver in said photosensitive stratum, reacting said silver halide solvent with unreduced silver halide in said photosensitive stratum to form a complex silver salt, and converting said complex silver salt to silver on one of said sheets.

References Cited in the file of this .patent UNITED STATES PATENTS 1,503,595 Mees Aug. 5, 1924 2,147,441 Holt Feb. 14, 1939 2,352,014 Rott June 20, 1944 2,543,181 Land Feb. 27, 1951 2,614,927 Broughton et a1 Oct. 21, 1952 2,627,459 Land Feb. 3, 1953 2,660,528 Schultz Nov. 24, 1953 2,662,822 Land Dec. 15, 1953 2,725,298 Yutzy et al Nov. 29, 1955 2,774,668 Rogers Dec. 18, 1956 FOREIGN PATENTS 814,449 France Mar. 15, 1937 930,369 France Aug. 4, 1947 647,922 Great Britain Dec. 28, 1950 OTHER REFERENCES Levenson: J. of Scientific Instruments, vol. 27, 1950, pages -171, 

